The side-effect that destroyed touch-screens as a mainstream input
technology despite a promising start in the early 1980s. It seems the
designers of all those spiffy touch-menu systems
failed to notice that humans aren't designed to hold their arms in front of
their faces making small motions. After more than a very few selections,
the arm begins to feel sore, cramped, and oversized — the operator
looks like a gorilla while using the touch screen and feels like one
afterwards. This is now considered a classic cautionary tale to
human-factors designers; “Remember the gorilla arm!” is
shorthand for “How is this going to fly in real
use?”.